The present invention relates to a load dissipating and limiting device for application in civil and industrial works having a high strength against seismic effects.
In the anti-seismic construction field, such as, for example, bridges, viaducts or buildings in general, there have been already used load dissipating and limiting devices, comprising specifically designed steel pegs which have elastic-plastic properties and which are usually interposed between the work or building proper and its supporting construction or foundation, so as to damp as far as possible stresses which, during a seismic event, are transmitted from the soil to the work.
However, it has been found that during the operation of these prior load dissipating and limiting devices, the elastic-plastic performance of the mentioned pegs is triggered not exclusively by seismic events but also by any mutual movements occurring between the two elements of the works which are connected to one another by the mentioned devices, such as, for example, under the effect of a different thermal expansion of the two elements of the works.
Actually, the mutual movements deriving from the thermal expansion generate an elastic-plastic deformation of the load dissipating devices, which is susceptible to limiting the deformation possibilities of said devices, in addition to greatly limiting the efficiency thereof in a case of a seismic event.
Moreover, since the mentioned thermal expansions can be considered as assimilable to reciprocating motions, even if of a very low speed, a reciprocating or alternating stress effect is generated which, involving the plastic deformation field of these devices, can spoil their satisfactory operation.
Moreover, in practically testing the above prior load dissipating devices, it has been found that the damping of the seismic wave is the greatest if the vibrating period of the work changes during the seismic vibration period.